In multiprogramming operating system (OS), objects are shared by users. These sh
ID: 3617935 • Letter: I
Question
In multiprogramming operating system (OS), objects are shared by users. These sharing can be managed by the OS in a centralized access control list. Describe a possible implementation of centralized access control list with an example four objects( OB-1, OB-2, OB-3, and OB-4), six users (USR-1, USR-2, USR-3, USR-4, USR-5, and USR-6) where each user have some access rights to at least two objects. Each object is owned by one user only. You can arbitrarily assign access rights of users to objects, but these access rights should be logical. [You can draw diagram and explain how it works].Explanation / Answer
The access control system regulates access to an object byassociating read (r), write (w), or execute (x)permissions with three categories of users as Owner, Group,Other
Owner of an object will be the one who createsit. And he will have all the three permission. He can modify thepermissions of the others.
So an owner will have the permissions as rwx.
For each object there will be one group. And some comes underthe other category and some users may not have any access to anobject.
Let us suppose the owners of the objects as, OB1 – USR1,OB2 – USR2, OB3 – USR3, OB4 – USR4.
Each owner can give permissions to members by dividing them intotwo categories of group and other.
Let OBJ1 has a group containing the users 2, 4, 5.
OBJ2 has a group containing the users 1, 3, 4, 6.
OBJ3 has a group containing the users 1, 2, 4.
OBJ4 has a group containing the users 3, 6.
The permissions given by the owners of each object to thesegroups of members be r-x.
That means, they are only given with permissions of reading andexecuting the object but not writing it.
Let the members in the others category are given a permission toexecute. i.e., --x
.
Following is the access control matrix showing the access controllist of some users and objects.
OB1
OB2
OB3
OB4
USR1
rwx
r-x
r-x
--x
USR2
r-x
rwx
r-x
-
USR3
-
r-x
rwx
r-x
USR4
r-x
r-x
--x
rwx
USR5
r-x
--x
--x
-
USR6
--x
r-x
--x
-
OB1
OB2
OB3
OB4
USR1
rwx
r-x
r-x
--x
USR2
r-x
rwx
r-x
-
USR3
-
r-x
rwx
r-x
USR4
r-x
r-x
--x
rwx
USR5
r-x
--x
--x
-
USR6
--x
r-x
--x
-
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